The present invention relates to a light signal control circuit for an image pick-up apparatus, for example, a stop control circuit having an automatic stop circuit for effecting stop correction which is effective when taking a picture against counter-light or the like where a great variation of brightness is involved.
Conventional stop control of an image pick-up apparatus has been performed by a method which combines a peak value system with an average value system. Such a conventional image pick-up apparatus is disclosed in JP-A-58-38075. FIG. 1 is a block diagram showing this conventional image pick-up apparatus. In FIG. 1, reference numeral 1 designates a stop, numeral 2 a lens, numeral 3 an image pick-up device such as a CCD, numeral 4 an amplifier circuit for amplifying a signal from the image pick-up device 3 and producing an image pick-up signal of a predetermined level, numeral 5 an analog-to-digital conversion circuit, numeral 6 a peak value detection circuit for detecting a peak value of the image pick-up signal, numeral 7 an average value detection circuit for detecting an average value of the image pick-up signal, numeral 8 a stop drive circuit for driving a stop, numeral 9 a signal processing circuit for effecting gamma processing or the like, and numeral 10 a digital-to-analog conversion circuit.
In a conventional image pick-up apparatus constructed as described above, the stop drive circuit 8 drives the stop 1 so that a sum of a signal from the peak value detection circuit 6 and an output signal from the average value detection circuit 7 becomes equal to a reference value "R" (shown in FIG. 1).
This conventional construction, however, has a disadvantage that an output signal of the peak value detection circuit becomes so large that the stop is closed undesirably to render an object dark when taking a picture of an object in an environment having a great brightness variation by including a light source or against counter-light.